For example, a fixing metal bracket which is adapted to fix a board mount connector on a circuit board by soldering is configured such that a surface thereof is generally applied with Sn (tin) plating in order to improve a soldering property. However, in a case where a fixing metal bracket applied with Sn plating is attached to a circuit board by soldering, an internal stress or an external stress is applied to a solder bonding portion so that a capillary crystal referred to as a whisker may be created. It is pointed out that a short circuit may possibly occur between the fixing metal bracket and a component around it by being caused by the whisker.
It is known that occurrence of a whisker is related to an internal stress or an external stress applied to an Sn plating layer as described above. Patent Document 1 discloses a technique in which a recessed portion having a depth which is 0.4 to 1.0 times of a thickness of the Sn plating layer is formed, and an internal stress or an external stress applied to the Sn plating layer is absorbed by the recessed portion, thereby suppressing occurrence of the whisker.